1. Field of the Invention
The invention relates to an improved pump element for a piston pump for generating high fuel pressure in fuel injection systems of internal combustion engines and to an improved piston pump employing the pump element.
2. Description of the Prior Art
In nearly all types of piston pumps, the rotary motion of a drive shaft is converted into an oscillating motion of the piston of a pump element. In so-called internally braced radial piston pumps for generating high fuel pressure in fuel injection systems of internal combustion engines, a plurality of pump elements are disposed, for instance radially to a drive shaft supported in a pump housing. The pistons of the pump elements are actuated by an eccentric portion of the drive shaft or by cams of the drive shaft. Because of the high pressures to which the fuel must be brought, the forces to be transmitted by the drive shaft to the pistons are very high. When the rotary motion of the drive shaft is converted into the oscillating motion of the pistons of the pump elements, forces between the drive shaft and the pistons occur that also act in the circumferential direction of the drive shaft. Similar effects also occur between the drive shaft and the pistons of in-line injection pumps or distributor injection pumps.
To reduce the wear between the pistons and the drive shaft, it is known from German Published, Nonexamined Patent Disclosure DE-OS 198 02 475 to provide a ring with flat faces, which does not rotate with the drive shaft, on the eccentric portion of the drive shaft of a radial piston pump. On the end of the piston toward the ring, a plate is provided in this radial piston pump. This plate is braced against the flat faces on the ring. When the pump elements are only partly filled in partial-load operation, the ring tends to rotate relative to the pump elements, because of the uneven load. The result is excessive loads on both the ring and the pump elements. These loads can lead to failure of a pump element or of the entire high-pressure fuel pump.